1. Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia
2. Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia
3. Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, Georgia
4. United States Public Health Service Commissioned Corps, Rockville, Maryland
5. Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia